MAGNETIZATION-GRID ROTATING-FRAME IMAGING TECHNIQUE FOR DIFFUSION ANDFLOW MEASUREMENTS

A method for NMR imaging of magnetization patterns generated by a prep aration radiofrequency pulse is reported. The technique is suitable fo r the simultaneous spatially and spectroscopically resolved acquisitio n of diffusion, flow, and spin-lattice relaxation data. The procedure is based on gradients of the RF amplitude B-1. A first preparation RF pulse produces a z-magnetization grid. After a certain evolution inter val, the grid is imaged by a rotating-frame imaging technique using th e same RF coil. Neither rotary nor Hahn echoes are intrinsic to the me thod. Transverse relaxation in the free-evolution intervals is irrelev ant. High-power transmitters in combination with suitable probeheads n ormally produce RF pulses which are short relative to transverse relax ation in the presence of RF, so that spin-lattice relaxation is the on ly time-limiting factor. Gradients of the main magnetic field induced by variations of the magnetic susceptibility are uncritical. The propo sed ''real-space detection'' method is compared with stimulated or rot ary-echo ''wave number encoding'' procedures for diffusion experiments . It is shown that the imaging procedure presented not only makes visi ble the spatial (apart from the spectral) distribution of transport pr operties which otherwise are concealed in the wave-number encoded sign al, but also renders the measuring procedure insensitive to inhomogene ities of the B, gradient, which needs neither to be constant nor to be uniformly oriented. Extremely inhomogeneous B, gradient distributions should even make single-scan diffusion experiments feasible. The magn etization-grid rotating-frame imaging procedure can be employed for th e two-dimensional measurement and representation of the probability P( z(1), O/z(2), t) that a particle is at a position z(1) at a time 0 and at a position z(2) at a time t. (C) 1995 Academic Press, Inc.